Generally speaking, since the ceramic product such as the ceramic condenser or the like must be baked at very high temperature of about 1,300 degrees centigrate, the vessel which contains such material must be made from such ceramic material to be good enough for such high temperature. And a carrier means or other means in a tunnel furnace must be good enough for such high temperature, too. But, as the ceramic product will easily be broken by a shock or mechanical force, such ceramic vessel can not be pushed out through the furnace by pushing means, also if shock or vibration is given to the material in the vessel during baking process, the product would happen inhomogenization therein.
In a conventional tunnel furnace, as a carrier means for transferring the vessels contained the material for product to be baked and heated, slide plate means as a carrier or an endless conveyer made from chain with a metal net attachment in exchange for the slide plate means is used. The slide plate must be made from peculiar brick by heat-resisting and unworn or untorm material, and the furnace floor boarding must be also made from such same special brick. In the furnace, many slide plates are connectingly provided on the furnace floor boarding, then the carrier is pushed in due course from an inlet side to an outlet side by a pushing means equipped with at out side of the inlet. In accordance with movement of the carrier, the vessels mounted on the carrier are forwarded and transferred through the tunnel furnace.
By this conventional method of transfer, the transfer means which mounted the vessels is entered in due order into the furnace from the inlet thereof and come out from the outlet, and after the sliding plate mounted the vessels come out the furnace, the empty vessels which the baked products was taken out therefrom and sliding plate for transfer means are recycled to the inlet through the out side of the furnace by means of an endless conveyer equipped with at out of the furnace. Therefore, enormous volume of heat releases from the carrier means during retransferring operation at the out side of the furnace, since the conventional apparatus is one way operation for recycling the carrier means. Consequently, further auxiliary heating in the furnace is required to heat the carrier means. Accordingly, heat energy for auxiliary heating is vainly spent in the conventional transfer means.
Also in the conventional furnace, since all of the carrier means is passed at the most high temperature center portion in the furnace and all of the carrier means is required to be made from heat-resisting material to endure the most high temperature, the cost for making the carrier means is very expensive. Further, sudden change in the temperature shortens the carriers' life, since the carriers are passed through the most high temperature portion and come out from the outlet, then the carriers cool by the atmosphere and are reentered from the inlet of the furnace in accordance with the recycle operation.
And then, in the conventional transfer method there are some important problems that, in case where the vessels are heaped up on the carrier means in the furnace providing the predetermined temperature characterization and the vessels receive heating or baking treatment, the heat to the lower vessel conducts to it through and after heating the carrier, therefore, effect for rising and falling the temperature to the lower vessel gets late in comparision with the upper vessels. The difference of the baking condition of the material between the heaped up vessels occurs. Especially, after heating the material up to the most high temperature, the homogenous products could not be obtained, because the lower vessel is over heated by heat of the carrier means.